Implantable medical devices are used to treat patients suffering from a variety of conditions. One example of an implantable medical device is a cardiac defibrillator used to treat patients suffering from ventricular fibrillation, also referred to as tachyarrhythmia. In operation, the defibrillator device constantly monitors the electrical activity of the heart of the patient, detects ventricular fibrillation, and in response to that detection, delivers appropriate shocks to restore normal heart rhythm. Shocks as large as 30-35 joules or more may be needed. The shocks are typically delivered from capacitors capable of providing that energy in a fraction of a second. To provide timely therapy when ventricular fibrillation is detected, the capacitors should be charged with sufficient energy in only a few seconds. As a result, the power source should have a high current rate capability to provide the necessary amount of energy to the capacitors in the limited amount of time, it should also have a low self-discharge rate to extend its useful life, and it should be highly reliable to provide the desired therapy when required. Typically, the power sources used in such devices are lithium electrochemical cells because they provide the desired characteristics identified above.
Implantable defibrillator devices are preferably designed with shapes that are easily accepted by the patient's body and which also minimize patient discomfort. As a result, the corners and edges of the devices are typically designed with generous radii to present a package having smoothly contoured surfaces. It is also desirable to minimize the volume occupied by the devices as well as their mass to further limit patient discomfort. As a result, the devices continue to become thinner, smaller, and lighter.
Known high current rate power sources used in implantable defibrillator devices employ prismatic, six-sided rectangular solid shapes in packaging of the electrode assemblies. Examples of such package shapes can be found in, e.g., U.S. Pat. No. 5,486,215 (Kelm et al.). Typical device layout includes two such power sources centrally located within the device.
Although the use of curved battery cases in implantable devices is known, they are typically found in devices requiring only low current rate discharge such as pacemakers. Batteries with curved cases have been used in connection with the high current rate batteries required for, e.g., implantable defibrillator devices. However, these high current rate batteries used thin, flat layered electrodes that do not package efficiently within curved cases.
Although not admitted as prior art, examples of battery designs can be found in the issued U.S. Patents listed in Table 1 below.
______________________________________ U.S. Pat. No. Inventor(s) Issue Date ______________________________________ 2,928,888 Vogt March 15, 1960 3,373,060 Gray March 12, 1968 3,395,043 Schoeld July 30, 1968 3,558,358 Ropp, Jr. January 26, 1971 4,051,304 Snook September 27, 1977 4,105,832 Sugalski August 8, 1978 4,332,867 Tsuda et al. June 1, 1982 4,335,191 Peled June 15, 1982 4,539,271 Crabtree September 3, 1985 4,539,274 Goebel September 3, 1985 4,550,064 Yen et al. October 29, 1985 4,565,752 Goebel et al. January 21, 1986 4,565,753 Goebel et al. January 21, 1986 4,663,247 Smilanich et al. May 5, 1987 4,664,989 Johnson May 12, 1987 4,668,320 Crabtree May 26, 1987 4,767,682 Dorogi et al. August 30, 1988 4,794,056 Pedicini December 27, 1988 4,830,940 Keister et al. May 16, 1989 4,863,815 Chang et al. September 5, 1989 4,963,445 Marple et al. October 16, 1990 5,439,760 Howard et al. August 8, 1995 5,443,925 Machida et al. August 22, 1995 5,458,993 Terao et al. October 17, 1995 5,458,997 Crespi et al. October 17, 1995 5,486,215 Kelm et al. January 23, 1996 5,549,717 Takeuchi et al. August 27, 1996 5,569,558 Takeuchi et al. October 29, 1996 5,603,737 Marincic et al. February 18, 1997 5,616,429 Klementowski April 1, 1997 ______________________________________
All patents listed in Table 1 above are hereby incorporated by reference in their respective entireties. As those of ordinary skill in the art will appreciate readily upon reading the Summary of the Invention, Detailed Description of the Preferred Embodiments and Claims set forth below, many of the devices and methods disclosed in the patents of Table 1 may be modified advantageously by using the teachings of the present invention.